RPN iterator

gistfile1.py

from collections import deque

from more_itertools import consumer


OPS = {'+': lambda a, b: b + a,
       '/': lambda a, b: b / a,
       '-': lambda a, b: b - a,
       '*': lambda a, b: b * a}


@consumer
def eval_rpn():
    """A consumer iterator that takes pieces of an RPN expression and yields
    the evaluated stack"""
    stack = []
    while True:
        i = yield stack
        op = OPS.get(i)
        stack.append(op(stack.pop(), stack.pop()) if op else i)


INPUT = [5, 15, '+', 4, '/']
rpn = eval_rpn()
stacks = (rpn.send(i) for i in INPUT)

# I think I'll add a last() to more_itertools so we don't have to do this less readable thing:
print deque(stacks, 1).pop()[0]

And without the hotdogging:

OPS = {'+': lambda a, b: b + a,
       '/': lambda a, b: b / a,
       '-': lambda a, b: b - a,
       '*': lambda a, b: b * a}


def eval_rpn(input):
    """A consumer iterator that takes pieces of an RPN expression and yields
    the evaluated stack"""
    stack = []
    for i in input:
        op = OPS.get(i)
        stack.append(op(stack.pop(), stack.pop()) if op else i)
    return stack[0]


print eval_rpn([5, 15, '+', 4, '/'])